The present invention relates to a drop-on-demand, or impulse, ink jet print head and in particular to a compact ink jet print head incorporating an array of ink jets each being driven by a separate driver.
Ink jet systems, and in particular drop-on-demand ink jet systems, are well known in the art. The principle behind an impulse ink jet is the displacement of an ink chamber and subsequent emission of ink droplets from the ink chamber through a nozzle. A driver mechanism is used to displace the ink in the ink chamber. The driver mechanism typically consists of a transducer (e.g., a piezoceramic material) bonded to a thin diaphragm. When a voltage is applied to a transducer, the transducer attempts to change its planar dimensions, but, because it is securely and rigidly attached to the diaphragm, bending occurs. This bending displaces ink in the ink chamber, causing the flow of ink both through an inlet from the ink supply to the ink chamber and through an outlet and passageway to a nozzle. In general, it is desirable to employ a geometry that permits multiple nozzles to be positioned in a densely packed array. However, the arrangement of ink chambers and coupling of ink chambers to associated nozzles is not a straight forward task, especially when compact ink jet array print heads are sought.
Some representative examples of the prior art will now be described.
Juliana, Jr., et al. U.S. Pat. No. 4,266,232 and Doring U.S. Pat. No. 4,312,010 each utilize a "reducer" section to converge channels leading from ink pressure chambers to nozzles to thereby achieve a more closely spaced array of nozzles. The use of a "reducer" section adds greatly to the thickness of an ink jet print head and adds to the complexity of manufacturing such print heads. In addition, the Doring patent discloses an array of nozzles with channels of differing lengths for coupling respective ink chambers to the associated nozzles. Because of the different length channels, ink jet print heads of this type will have varying jetting characteristics from the different nozzles. Costly drive circuitry which drives the various piezoelectric transducers differently to compensate for differences in channel length can be used, but uniform ink drop ejection from the varying nozzles is nevertheless difficult to achieve.
Stemme U.S. Pat. No. 3,747,120 (for example see FIG. 20) discloses still another ink jet print head design. In this design, respective rows of 2, 3 and 2 circular ink pressure chambers are arranged with staggered centers. Channels of unequal length couple the respective ink pressure chambers to a common ink chamber. The nozzles are in communication with this common ink chamber. In addition to other drawbacks, the use of a common ink chamber between the nozzles and channels allows acoustic cross talk between individual nozzles.
Doring, et al. U.S. Pat. No. 4,599,628 discloses a further ink jet print head structure having an array of nozzles. In this construction, a generally conically shaped ink pressure chamber couples the respective nozzles to a common ink supply. These pressure chambers are of circular cross section and are arranged in two parallel rows with the centers of the pressure chambers of one row being aligned with the centers of the pressure chambers of another row.
Another exemplary ink jet print head construction is shown in Cruz-Uribe, et al. U.S. Pat. No. 4,680,595 With reference to FIGS. 1, 3, 5 and 6 of this patent, two parallel rows of generally rectangular ink pressure chambers are shown with their centers aligned. Ink jet nozzles are each coupled to a respective associated ink pressure chamber. The central axis of each nozzle in this design extends normal to the plane containing the ink pressure chambers and intersects an extension portion of the ink pressure chamber. Also, ink is supplied to each of the chambers through a restrictive orifice that is carefully formed to match the nozzle orifice. In general, for ink of a particular viscosity and for a given drop ejection rate, a rectangular piezoceramic transducer having a greater surface area is required than in the case of a round or hexagonal piezoceramic transducer if the two types of jets are to be operated at the same drive voltage. In addition, due to the construction employed in this prior art ink jet array, the packing of ink chambers for a given size ink jet is limited.
Kanayama U.S. Pat. No. 4,460,906 describes an ink jet print head with a circular ink pressure chamber having an offset channel which connects the pressure chamber to a nozzle. In this ink jet print head, ink is ejected in a direction perpendicular to the plane of the ink pressure chambers. A pool of ink covers the outer surface of each nozzle through which the ink is jetted. Ink is supplied other than through an associated ink pressure chamber and thus this design is somewhat similar to Stemme U.S. Pat. No. 3,747,120 discussed above.
U.S. Pat. Nos. 4,216,477 to Matsuda, et al. and 4,525,728 to Koto are representative of ink jet designs in which ink is ejected parallel to, instead of perpendicular to, the plane of the ink pressure chambers. In general, prior art array ink jet print heads in which the nozzle axes are parallel to the plane of the transducers are relatively complex to manufacture. Connecting channels lead from individual ink pressure chambers to ink drop ejection nozzles. In the Koto patent, a row of rectangular transducers is mounted on one side of a substrate with another row of such transducers being mounted to the opposite side of the substrate. The transducers and associated nozzle openings on one side of the substrate are staggered with respect to those on the other side of the substrate to increase the packing density. In the Matsuda, et al. patent, each rectangular transducer is respectively coupled to an ink chamber which communicates through a passageway to a nozzle orifice. In at least some embodiments described in this patent, these passageways are of different length, depending upon the location of the transducer relative to its associated nozzle. Fishbeck, et al. U.S. Pat. No. 4,584,590 illustrates in FIGS. 3 and 4 still another ink jet print head array in which ink drops are ejected in a direction parallel to the plane of the rectangular transducers used to expand and contract the volume of an ink chamber. Other examples of constructions which eject ink droplets parallel to the plane of transducers or ink pressure chambers are shown in U.S. Pat. No. 4,435,721 of Tsuzuki; U.S. Pat. No. 4,528,575 to Matsuda; U.S. Pat. No. 4,521,788 of Kamura and D.E. U.S. Pat. No. 3,427,850 of Yamamuro.
Although there are a number of prior art ink jet print heads with an array of ink jets, a need exists for improved ink jet print heads of this type which are compact, relatively easy to manufacture, capable of high drop speed operation, and which are efficient.